1. Field of the Invention
The present invention relates to in-vehicle input devices, and in particular, relates to an in-vehicle input device that can be operated with a touch panel disposed on a steering wheel.
2. Description of the Related Art
In-vehicle input devices including touch panels instead of mechanical input units have recently been developed. Such an input device has a switch operation area disposed on a steering wheel to provide layout flexibility and a flat appearance. Touch panel input devices are widely used mainly for mobile apparatuses. Such a touch panel input device detects an input operation based on a change in capacitance caused when an operator operating a mobile apparatus moves their finger closer to an operation surface of the input device.
If such a touch panel input device for a mobile apparatus is used for an in-vehicle apparatus, the input device may be erroneously operated in response to the motion of a driver driving a vehicle. For example, if the driver rotates a steering wheel provided with the touch panel input device in order to turn the vehicle, their hand and fingers will move over an operation surface of a touch panel. Unfortunately, an unintended operation may be performed, causing a safety problem.
As a typical in-vehicle touch panel input device that is less likely to be erroneously operated, Japanese Unexamined Patent Application Publication No. 2002-225724 discloses an operation device for in-vehicle apparatuses. The operation device will now be described with reference to FIG. 10.
The operation device, indicated at 900, includes a steering wheel 901 for steering a vehicle, a display 904 for displaying an operation mode image 913 for the in-vehicle apparatuses, a touch panel 907 that a driver can give input to or operate by touching, and a display/load controller (control unit) 909. The display 904 is disposed on an instrument panel 902 of the vehicle so as to face the steering wheel 901. The touch panel 907 is disposed on the steering wheel 901 and serves as a light-transmissive window 916 through which the driver can view the operation mode image 913. The display/load controller 909 outputs operation information to an in-vehicle apparatus in response to an input operation on the touch panel 907 only while the steering wheel 901 is held in a straight-ahead driving position or in the vicinity of this position.
The operation device with such a configuration substantially rejects input operations on the touch panel while the driver rotates the steering wheel, thus preventing an erroneous operation during driving. This achieves safety. In addition, the light-transmissive touch panel allows the driver to view the display, thus maintaining visibility.
In the operation device 900, however, any input operation cannot be performed while the driver rotates the steering wheel. If the steering wheel is in the straight-ahead driving position, a likelihood that the touch panel may be erroneously operated will still remain because the driver may unconsciously move part of their body over the touch panel while driving, for example, while driving in a forward-leaning posture or while driving with one hand on upper part of the steering wheel. Furthermore, the driver may wear gloves while driving in, for example, a cold climate area. The gloves insulate fingers from an electrode of the touch panel. If the driver moves their gloved finger closer to the operation surface of the touch panel, a capacitance will not be formed between the gloved finger and the electrode of the touch panel. Unfortunately, the touch panel cannot be operated.